The present invention relates to a process for preparing substituted olefins by self metathesis or cross metathesis.
Olefin metathesis (disproportionation) involves, in its simplest form, a reversible, metal-catalyzed transalkylidenation of olefins by rupture and reformation of carbon-carbon double bonds. In the case of the metathesis of acyclic olefins, a distinction is made, for example, between a self metathesis in which an olefin is transformed into a mixture of two olefins having different molar masses (for example, conversion of propene into ethene and 2-butene) and cross metathesis or co-metathesis which describes a reaction of two different olefins (for example, reaction of propene with 1-butene to give ethene and 2-pentene). Further application areas of olefin metathesis include syntheses of unsaturated polymers by ring-opening metathesis polymerization (ROMP) of cyclic olefins and acyclic diene metathesis polymerization (ADMET) of xcex1,xcfx89-dienes. Relatively new applications are the selective ring opening of cyclic olefins with acyclic olefins and also ring closure reactions (RCM) by means of which, preferably starting from xcex1,xcfx89-dienes, unsaturated rings of various ring sizes can be prepared.
Catalysts suitable for metathesis reactions are, in principle, homogeneous and heterogeneous transition metal compounds.
Heterogeneous catalysts, for example molybdenum, tungsten or rhenium oxides on inorganic oxidic supports, display high activity and regenerability in reactions of nonfunctionalized olefins, but must frequently be pretreated with an alkylating agent to increase the activity when functionalized olefins such as methyl oleate are used. Olefins containing protic functional groups (for example hydroxyl groups, carboxyl groups or amino groups) lead to spontaneous deactivation of the heterogeneous catalyst.
The present invention concerns a process for preparing bifunctionalized C6-hydrocarbons of the ECH2CHxe2x95x90CHCH2E type, for example adipic acid and derivatives thereof, with a metathesis reaction of an olefin of the RCHxe2x95x90CHCH2E type being carried out as key step for forming the C6 unit. 
C6-Hydrocarbons of this type are, after functionalization, industrially important precursors and intermediates: adipic acid serves, for example, as precursor for the production of nylon 6.6 (fiber sector) and has hitherto been prepared mostly by oxidative cleavage of cyclohexane. More recent developments involve formative reactions for adipic acid from butadiene, for example by the Monsanto process by carbonylation of the intermediate 1,4-dimethoxy-2-butene and in the BASF process by two-stage carbonylation of butadiene in the presence of methanol.
The two-stage carbonylation requires drastic reaction conditions and gives, starting from butadiene, only quite moderate yields of adipic acid, namely about 70% over the two stages.
The abovementioned metathesis reaction therefore appears to be a possible alternative route to the desired compounds.
The generally high activity of homogeneous metathesis catalysts in respect of olefins is drastically reduced when using electron-depleted olefins such as acrylic acid or their derivatives. In particular, self metathesis reactions of olefins of the RCHxe2x95x90CH(CH2)nE type to form RCHxe2x95x90CHR and E(CH2)nCHxe2x95x90CH(CH2)nE become problematical in the presence of the known metathesis catalysts when E is an electron-withdrawing substituent, n is zero or 1 and Rxe2x95x90H, alkyl or aryl. Use of substituted olefins such as methyl 3-pentenoate, 3-pentenoic acid or 3-pentenonitrile in self metathesis reactions is consequently accorded little mention in the literature because of unsatisfactorily low activity.
J. Chem. Soc., Chem. Commun. 1983, 262-263, J. Chem. Soc., Chem. Commun. 1981, 1081-1082 and J. Organomet. Chem. 1985, 280, 115-122, describe the self metathesis of unsaturated nitrites of the CH2xe2x95x90CH(CH2)nCN type in the presence of heterogeneous Re2O7/Al2O3 catalysts which have been activated with SnMe4 or SnEt4. While 4-pentenonitrile is reacted in a yield of up to about 90%, allyl cyanide does not undergo any productive metathesis reactions with the exception of isomerization to form crotononitrile.
Recl. Trav. Chim. Pays-Bas 1977, 96(11), 86-90, describes metathesis reactions of low molecular weight unsaturated esters using the homogeneous catalyst system WCl6/SnMe4. Although methyl 3-pentenoate is reacted with a selectivity of 95% to form 2-butene and the dehydroadipic ester in the presence of 2 mol % of WCl6/SnMe4, a disadvantage is the high sensitivity of the catalyst system toward impurities in the feed. Metathesis reactions using unsaturated acids are not possible when the catalyst system mentioned is employed.
J. Mol. Catal. 1992, 76, 181-187, is concerned with the metathesis of functionalized olefins using the catalyst system WCl6 (or WOCl4) /1,1,3,3-tetramethyl-1,3-disilacyclobutane (DSBC). In the best experiment using WOCl4/DSBC, methyl 4-pentenoate is converted with a selectivity of 94% at conversions of 54% into the corresponding C8-diester. In the presence of the same catalyst system, allyl cyanide is converted with a selectivity of 82% at a conversion of 53% into dehydroadipodinitrile with elimination of ethene.
Chem. Lett. 1976, 1021-1024, describes the self metathesis of methyl 4-pentenoate in a conversion of 60% when using WCl6/Me2Al2Cl2.
It is an object of the present invention to develop an economically attractive synthetic route to bifunctionalized C6-hydrocarbons from readily accessible starting materials under moderate reaction conditions using a suitable, generally usable catalyst system.
We have found that this object is achieved by a process for preparing C6 compounds of the formula (I)
Exe2x80x94CH2xe2x80x94CHxe2x95x90CHxe2x80x94CH2xe2x80x94E1xe2x80x83xe2x80x83(I)
by self metathesis or cross metathesis of compounds of the formulae (II) and/or (III)
Rxe2x80x94CHxe2x95x90CHxe2x80x94CH2xe2x80x94Exe2x80x83xe2x80x83(II)
R1xe2x80x94CHxe2x95x90CHxe2x80x94CH2xe2x80x94E1xe2x80x83xe2x80x83(III)
where
E, E1 are independently xe2x80x94CHO, xe2x80x94COOH, xe2x80x94COOR2, xe2x80x94C(O)NR3R4, xe2x80x94CN,
R, R1 are independently H, C1-12-alkyl, C6-12-aryl or C7-13-alkylaryl and
R2, R3, R4 are independently H, C1-12-alkyl, C7-13-aralkyl,
in the presence of a homogeneous catalyst comprising ruthenium compounds or ruthenium complexes.
Accordingly, the object is achieved according to the present invention by a process sequence in which the key step for forming a C6-hydrocarbon of the ECH2CHxe2x95x90CHCH2E type is a self metathesis reaction of an olefin of the RCHxe2x95x90CHCH2E type according to the following equation: 
As coproduct, RCHxe2x95x90CHR is formed in stoichiometric amounts and can, if desired, be processed further by subsequent reactions. For example, xcex1-olefins of the CH2xe2x95x90CHR type can be obtained by ethenolysis of RCHxe2x80x94CHR.
In the above equation, E is an aldehyde, ester, acid, acid amide or nitrile function. R is hydrogen or an alkyl, aryl or alkylaryl radical. Preferred alkyl radicals R are linear C1-6-alkyl radicals, e.g. methyl or ethyl, or branched C1-6-alkyl radicals in which the branching point is at least one methylene group away from the double bond.
It is also possible to react substrates having different radicals R, R1 and E, E1 with one another in a cross metathesis reaction. In this case, mixed reaction products have to be expected. 
Preferably, Exe2x95x90Exe2x80x2 and Rxe2x95x90Rxe2x80x2. E and Exe2x80x2 are particularly preferably ester or carboxyl groups. R and Rxe2x80x2 are preferably methyl or ethyl groups.
The process of the present invention is carried out in the presence of a homogeneous catalyst comprising ruthenium compounds or ruthenium complexes. Preference is given to using ruthenium-alkylidene complexes as catalyst. The ruthenium-alkylidene complexes are preferably selected from among 
where
B can be stabilized by a further ligand L4 and
X is an anion which does not coordinate or coordinates only weakly to the metal center,
Y is a monodentate or polydentate anionic ligand,
R and Rxe2x80x2 are each, independently of one another, hydrogen or a substituted or unsubstituted C1-20-alkyl, C6-20-aryl or C7-20-alkylaryl radical and
L1, L2, L3 and L4 are, independently of one another, uncharged electron donor ligands, or
ruthenium complexes of the formulae C or D
RuXxe2x80x2Yxe2x80x2(xe2x95x90CHxe2x80x94CH2Rxe2x80x3)L1L2xe2x80x83xe2x80x83(C)
RuXxe2x80x2Yxe2x80x2(xe2x95x90CHRxe2x80x3))L1L2xe2x80x83xe2x80x83(D)
xe2x80x83where
Xxe2x80x2, Yxe2x80x2 are identical or different anionic ligands,
Rxe2x80x3 is hydrogen or a substituted or unsubstituted C1-20-alkyl radical or C6-20-aryl radical, and
L1 and L2 are, independently of one another, uncharged electron donor ligands.
The uncharged electron donor ligands are preferably phosphines, arsines, stibines containing at least two bulky groups, amines, pyridines, xcfx80-coordinated olefins or solvent molecules. The uncharged electron donor ligands are particularly preferably selected from among phosphines of the formula PRaRbRc in which Ra and Rb are, independently of one another, phenyl radicals or sterically hindered organic radicals and Rc is hydrogen or a substituted or unsubstituted C1-12-alkyl radical or C6-20-aryl radical or is as defined for Ra.
Ra and Rb are preferably selected from among i-propyl, tert-butyl, cyclopentyl, cyclohexyl, phenyl or menthyl.
Such complexes are described, for example, in WO 93/20111, WO 96/04289, WO 96/06185, WO 97/03096, and also in DE-A-197 36 609 and DE-A-198 00 934.
The cationic catalyst systems comprise as active components cationic ruthenium complexes of the formula A (cationic carbyne complexes) or B (cationic carbene complexes) or mixtures comprising them 
where B can be stabilized by a further ligand L4.
In the structures A and B,
Xxe2x88x92 is an anion which does not coordinate or coordinates only weakly to the metal center, for example a complex anion from main groups III to VII of the Periodic Table of the Elements, e.g. BRxe2x80x34xe2x88x92 (Rxe2x80x3xe2x95x90F, phenyl which may bear one or more fluorine atoms or perfluorinated C1-6-alkyl radicals as substituents, e.g. C6H5xe2x88x92nFn where n=1 to 5), PF6xe2x88x92, AsF6xe2x88x92, SbF6xe2x88x92, ClO4xe2x88x92, CF3SO3xe2x88x92 or FSO3xe2x88x92,
Y is a monodentate or polydentate anionic ligand,
R and Rxe2x80x2 are each, independently of one another, hydrogen or a substituted or unsubstituted C1-20-alkyl, C6-20-aryl or C7-20-alkylaryl or -aralkyl radical, and
L1, L2, L3 and L4 are, independently of one another, uncharged electron donor ligands, preferably nitrogen donors such as amines and pyridines, phosphines, arsines, stibines containing at least two bulky groups such as i-propyl, t-butyl, cyclopentyl, cyclohexyl, menthyl or the like, or else xcfx80-coordinated olefins or solvent molecules.
The radicals preferably have the following meanings:
Xxe2x88x92 is BRxe2x80x34xe2x88x92 where Rxe2x80x2=F or C6H3 (mxe2x88x92CF3)2,
Y is halogen, preferably chlorine, or OR where R=C1-6-alkyl, C6-12-aryl, preferably phenoxide,
R is H,
Rxe2x80x2 is C1-6-alkyl, C6-12-aryl, C7-20-aralkyl, preferably methyl or benzyl,
L1, L2 are phosphines containing at least two bulky groups,
L3, L4 are cyclic or acyclic ethers or tertiary amines such as NMe2phenyl, NMe3, NEt3.
The synthesis of the active components A and/or B or of mixtures comprising these active components can be carried out starting from numerous organometallic starting materials, for example
by reaction of hydrido(vinylidene) complexes of the RuY(H) (xe2x95x90Cxe2x95x90CHR)L1L2 type which can be synthesized by reacting RuClH(H2)L1L2 with terminal alkynes HCxe2x95x90CR, with R+Xxe2x88x92, where Xxe2x88x92 is a noncoordinating or weakly coordinating anion. RuClH(H2)L2 can be prepared by literature methods, for example from the polymeric ruthenium precursor [RuCl2(COD)]x (COD=cyclooctadiene) in i-propanol in the presence of L under a hydrogen atmosphere (Werner et al., Organometallics 1996, 15, 1960 to 1962) or starting from the same starting material in sec-butanol in the presence of L and tertiary amines (NEt3) under a hydrogen atmosphere (Grubbs et al., Organometallics 1997, 16, 3867 to 3869). RuClH(H2)L2 can also be obtained starting from RuCl3.H2O in THF by reaction with L in the presence of activated magnesium under a hydrogen atmosphere (BASF AG, DE-A-198 00 934 which has earlier priority but is not a prior publication) and is preferably reacted in situ with 1-alkynes to give the corresponding hydrido(chloro)vinylidene complexes RuClH(xe2x95x90Cxe2x95x90CHR)L2. The latter can be isolated or reacted in situ with H+Xxe2x88x92 (Xxe2x88x92=noncoordinating anion) to give the active components A and/or B used according to the present invention.
By reaction of compounds of the RuYYxe2x80x2 (xe2x95x90CHR)L1L2 type (where Y can be the same as Yxe2x80x2) with R+Xxe2x88x92, where Xxe2x88x92 is a noncoordinating or weakly coordinating anion. Mixed anionic alkylidene complexes RuXY(xe2x95x90CHCH2R)L2 can be prepared as described in DE-A-198 00 934 starting from RuXH(xe2x95x90Cxe2x95x90CHR)L2.
By reaction of compounds of the RuYYxe2x80x2(xe2x95x90CHR)L1L2 type with anion-abstracting metal salts M+Xxe2x88x92 or Lewis acids such as BF3 or AlCl3 in the presence of a ligand L3, where Xxe2x88x92 is a noncoordinating or only weakly coordinating anion and the anionic ligands Y and Yxe2x80x2 can be identical or different. MX can, for example, be AgPF4, AgB(C5F5)4, AgPF6 or AgSbF6. R+Xxe2x88x92, M+Xxe2x88x92 and the corresponding Lewis acids are preferably used in a molar ratio to the organometallic starting material of from 1:10 to 1000:1.
The reactions to form the active components A and/or B are preferably carried out in organic solvents under an inert gas atmosphere, preferably in solvents which can stabilize an unsaturated metal center by coordination, for example aliphatic or cyclic ethers such as dioxane or THF, amines, DMSO, nitriles, phosphines, arsines, stibines, water, olefins or other two-electron donors. The reaction is preferably carried out in THF at from xe2x88x92100 to +100xc2x0 C., preferably from xe2x88x9280 to xe2x88x9240xc2x0 C., and pressures from 1 mbar to 100 bar, preferably from 0.5 to 5 bar.
The reaction can be carried out using one or more molar equivalents of R+Xxe2x88x92. L1-3RX formed when using excess R+Xxe2x88x92 does not have an adverse effect on the reaction. The resulting compositions comprising the active components A and/or B can be used in situ as a highly active metathesis catalyst system or can be stored at low temperatures under an inert gas atmosphere. The active components A or B can, if desired, be used in isolated form.
As a rule, the reaction is complete after from 1 s to 10 h, preferably after from 3 s to 1 h. Suitable reaction vessels are generally glass or steel vessels which may, if desired, be lined with ceramic.
The preparation of the ruthenium complexes of the formula (C)
RuXxe2x80x2Yxe2x80x2 (xe2x95x90CHxe2x80x94CH2Rxe2x80x3)L1L2xe2x80x83xe2x80x83(C)
where
Xxe2x80x2, Yxe2x80x2 are identical or different anionic ligands,
Rxe2x80x3 is hydrogen or a substituted or unsubstituted C1-20-alkyl radical or C6-20-aryl radical and
L1 and L2 are, independently of one another, uncharged electron donor ligands,
is preferably carried out by
(a) reacting RuX3 with L1 and L2 in an inert solvent in the presence of a reducing agent and hydrogen and compounds of the formula IV
Rxe2x80x3xe2x80x94Cxe2x89xa1CHxe2x80x83xe2x80x83(IV)
where Rxe2x80x3 is as defined above, in the presence or absence of water,
xe2x80x83to give a compound of the formula V
RuXxe2x80x2H(xe2x95x90Cxe2x95x90CHRxe2x80x3)L1L2xe2x80x83xe2x80x83(V)
where Xxe2x80x2, Rxe2x80x3, L1, L2 are as defined above,
(b) separating the compound of the formula V from the reaction mixture and subsequently reacting it in an inert solvent with HYxe2x80x2, (HL1)Yxe2x80x2 or (HL2)Yxe2x80x2 and compounds of the formula IV
Rxe2x80x2xe2x80x94Cxe2x89xa1CHxe2x80x83xe2x80x83(IV)
where Rxe2x80x3 is as defined above, in the presence or absence of water,
(c) subsequently reacting the product with HYxe2x80x2, [HL1]Yxe2x80x2 or [HL2]Yxe2x80x2.
It has been found that the above ruthenium complexes can be obtained in very good yields directly from RuXxe2x80x23, preferably RuCl3.3(H2O), by simple reaction with ligands L1 and L2, hydrogen and terminal alkynes of the formula IV in the presence of reducing agents without isolation of intermediates. These ruthenium complexes have no vinylic substituents on the carbene carbon atom. The starting materials can be prepared inexpensively and are readily available.
To prepare mixed anionic complexes of the formula (C), the intermediate of the formula V is obtained or isolated and subsequently reacted further. This enables different ligands Xxe2x80x2 and Yxe2x80x2 to be introduced.
The first stage of the synthesis is the reaction of RuXxe2x80x23 with the ligands L1 and L2 in an inert solvent in the presence of a reducing agent and hydrogen. Solvents which can be used are aromatics, heteroaromatics, cyclic or acyclic ethers. Preferred solvents are toluene, NMP, tetrahydrofuran, dialkyl ethers, glycol ethers and dioxane. Particular preference is given to tetrahydrofuran.
As reducing agent, it is possible to use any reducing agent which reduces Ru(III) to Ru(II) under the reaction conditions. The reduction is preferably carried out using hydrogen in the presence of a metallic or nonmetallic reducing agent, preferably in the presence of an alkali metal, an alkaline earth metal or a transition metal such as palladium or zinc which is present in metallic form and/or can be applied to a support. The alkaline earth metals, preferably magnesium, are preferably used in an activated form. The activation can be achieved, for example, by contacting with a chlorine-containing organic solvent. For example, in a single-vessel reaction under an inert gas atmosphere, magnesium can be placed in a diluted chlorine-containing organic solvent, for example dichloroethane, in the reaction vessel and, after an induction period of from one second to 10 hours, preferably from one minute to one hour, reacted with the solvent, RuXxe2x80x23 and the ligands L1 and L2 under a hydrogen atmosphere. The temperature in this reaction step (a) is preferably from 0 to 100xc2x0 C., particularly preferably from 20 to 80xc2x0 C., in particular from 40 to 60xc2x0 C. The pressure is preferably from 0.1 to 100 bar, particularly preferably from 0.5 to 5 bar, in particular from 0.8 to 1.5 bar. The reaction is carried out for a period of preferably from 10 minutes to 100 hours, particularly preferably from one hour to 10 hours. The molar ratio of ligands L1 and L2 together to the ruthenium salt used is preferably 2-20:1, particularly preferably 2-5:1. After the reaction in step (a), the reaction mixture is preferably at a temperature in the range from xe2x88x9280 to 100xc2x0 C., particularly preferably from xe2x88x9240 to 50xc2x0 C., in particular from xe2x88x9230 to 20xc2x0 C., with a 1-alkyne. Here, the molar ratio of ruthenium salt originally used to 1-alkyne is preferably from 1:1 to 1:10. The reaction is preferably carried out at a pressure of from 0.1 to 10 bar, particularly preferably from 0.8 to 1.5 bar, in particular from 1 to 1.4 bar, for a period of preferably from 30 seconds to 10 hours, particularly preferably from one minute to one hour. In the ruthenium complexes of the formula (C), Xxe2x80x2 is a monodentate anionic ligand, for example halogen, pseudohalogen, carboxylate, diketonate. Xxe2x80x2 is particularly preferably halogen, in particular bromine or chlorine, especially chlorine. The reaction is particularly preferably carried out using RuCl3.3H2O.
In the ruthenium complexes of the formula (C), Yxe2x80x2 can be the same ligand as Xxe2x80x2. It is preferably a halogen different from Xxe2x80x2 or a carboxyl group bound to a polymer or a support, which makes it possible to fix the catalyst to a support. The ligand Xxe2x80x2 in the intermediates of the formula V can be replaced by salt metathesis with MYxe2x80x2, where M is an alkali metal or ammonium, preferably potassium. This also makes it possible to obtain product mixtures.
L1 and L2 are, as described above, uncharged electron donor ligands. The radical R is hydrogen or a substituted or unsubstituted C1-20-, preferably C1-6-alkyl radical or C6-20-, preferably C6-8-aryl radical. Particularly preferred ruthenium complexes of the formula (C) are the complexes RuCl2(xe2x95x90CHxe2x80x94CH3) (PCy3)2 and RuCl2(xe2x95x90CHxe2x80x94CH2xe2x80x94Ph) (PCy3)2, where Cy is a cyclohexyl radical and Ph is a phenyl radical.
The ruthenium complexes of the formula
RuXxe2x80x22(xe2x95x90CHxe2x80x94CH2Rxe2x80x3)L1L2
where
Xxe2x80x2 is an anionic ligand,
Rxe2x80x3 is hydrogen or a substituted or unsubstituted C1-20-alkyl radical or C6-20-aryl radical, and
L1 and L2 are, independently of one another, uncharged electron donor ligands,
can also be obtained by
a) reacting RuXxe2x80x23 with a diene in a solvent based on one or more aliphatic secondary alcohols in the presence or absence of a reducing aid, and then with L1 and L2 in the presence of at least one coordinating weak base and hydrogen, and, without isolating intermediates,
b) subsequently reacting the product with compounds of the formula
Rxe2x80x3xe2x80x94Cxe2x89xa1CH
where Rxe2x80x3 is as defined above, in the presence of a soluble chloride source.
Compared to the catalyst systems described in the prior art, the ruthenium complexes used according to the present invention enable, inter alia, high selectivities together with comparatively long catalyst operating lives to be achieved even at very low catalyst concentrations (100 ppmxe2x80x941%) under mild reaction conditions (T=0-200xc2x0 C., p=1 bar absolute).
When using internal olefins RCHxe2x95x90CHCH2E in which R=Me or Et, the introduction of ethylene may be necessary or at least helpful for increasing the conversion in accordance with the following equation. In this case, ethylene can be used as stripping gas. 
The addition of solvents, for example pentane, acetone, ether and toluene, is not necessary in any of the reactions described, but it has no adverse effect on the reaction either.
The reactions are carried out at from 0 to 200xc2x0 C. and pressures of from 0.01 to 100 bar and are generally complete after from 10 minutes to 100 hours.
The reactions can be carried out continuously or batchwise in reactors such as glass vessels, reaction tanks, tube reactors or circulation reactors. Since the reactions are equilibrium reactions, it is advantageous to remove the process products from the equilibrium as quickly as possible in order to achieve a very high conversion. This is particularly useful for reactions in which low boilers such as ethene, 2-butene or propene are formed as coproducts.
To isolate the process products, the reaction mixture, which may comprise catalyst dissolved or suspended in the process product, is worked up by distillation and the process product can be isolated after a fine distillation. The catalyst-containing distillation bottoms can be returned to the reaction. The catalyst can also be recycled in a high-boiling solvent. It is also conceivable for the process of the invention to be performed in a reactive distillation apparatus in order to remove low-boiling components formed in situ from the equilibrium so as to maximize the conversion.
The compounds of the RCHxe2x95x90CHCH2E type (R and E, see above) used as starting materials for the metathesis reaction can be obtained, for example, in high yields from readily available starting materials such as dienes, for example butadiene, by hydroformylation, carbonylation or hydrocyanation.
The further processing of the bifunctionalized C6-hydrocarbons present in the metathesis product can be carried out by, inter alia, hydrogenation, hydroformylation, reductive amination, oxidation or ring closure.